With the advent of decoratively clad, or faced, sheet materials, they were immediately adopted for use in making table tops, furniture cabinets, countertops, kitchen cabinets and the like. Because of the decorative finish on the face of these materials, they require no finishing after they are assembled. Moreover, they are extremely durable.
Such materials utilize a strength providing base, or substrate, such as plywood, fiberboard or other composition board faced with a thin sheet, or veneer, of decorative film or wood bonded to the base. The facing is often only a few thousandths of an inch thick, and the base is usually an eighth, a quarter or some other dimensional fraction of an inch standard to structural materials.
This composite material is manufactured in modular dimensional sheets such as four by eight, four by twelve or the like, and is accordingly rather flexible. To construct items having finished surfaces in more than one plane from this material, it was historically necessary to assemble planar components of the item formed from the material with the finish veneer facing in the proper direction and join the corners in a mitered fit in order to prevent the unfinished edges of the base from showing. However, in even the most meticulously mitered joints the joinder line of the thin, finish veneer stands out as an unsightly reminder that the material is a facsimile of that apparent from the design of the facing. This is especially noticeable when the facing simulates a wood grain.
Further complications are attendant upon accurately rabbeting or grooving such laminar sheet materials because the variation in the thickness of the base may be in the range of twenty to thirty thousandths of an inch and the thickness of the facing to which the cut must extend is on the order of one tenth that amount.
These difficulties were obviated, and the usefullness of this sheet material was enhanced by the ability to fold the sheet material and thus form a construction that presents a continuous finished surface in more than one dimension. As disclosed in U.S. Pat. No. 3,456,701, an angular fold can be formed in the sheet material by accurately mitering a groove in the back of the sheet material and then bending the sheet to form an angular fold and at the same time maintaining a continuous unbroken continuity in the facing even after the sheet material has been folded along the groove.
In many applications it is desirable either for aesthetic or functional reasons to employ a fold that presents a curvilinear surface instead of the linear intersecting surfaces presented by the angular folding technique disclosed in the said U.S. Pat. No. 3,456,701. However, it is also highly desirable that the fold which results in the presentation of a curvilinear surface provide two properties inherent to the prior art fold which presents the linear intersecting surfaces--i.e., the properties of stability and further machinability.